Earth retaining walls are frequently constructed from stacked precast concrete blocks. After the blocks are stacked on a suitable foundation, the earth side of the wall is filled with backfill. The maximum height of the retaining is limited by a number of factors, including the size and weight of the blocks, the foundation for the wall, the type of backfill and surrounding earth, and drainage. It is well known that a higher retaining wall can be constructed if the wall is secured to the adjacent earth with a geogrid system.
Various types of systems have been used in the past for stabilizing concrete block earth retaining walls. In one type of system, ground anchors are embedded in the earth behind the retaining wall and are connected through cables or rods to the wall to prevent the wall from moving. In another type of geogrid system, a perforated geogrid fabric is buried in the earth behind the wall. After one or more tiers of blocks are stacked to form a portion of the wall, backfill is added behind the wall to substantially the level of the top of the stack. The fabric is laid over the backfill and over the top of the adjacent blocks. The next tier of blocks are then stacked on the wall on top of the fabric. Different types of fabric have been used in geogrid systems of this type, including metal fabrics and fabrics formed from a tough, stable synthetic resinous material. The fabric is formed with sufficient openings or perforations to allow water to freely pass through the fabric, and to help the fabric to grip the adjacent soil.
U.S. Pat. No. 6,416,257 shows a geogrid system in which a groove is formed across the top of each block to extend parallel to the face of the block. The bottoms of the blocks forming an adjacent upper tier include a projection which extends part way into the groove. A geogrid fabric is laid over the top of the blocks in a tier and an elongated flat member is inserted into the groove, forcing the fabric into the groove. When a block is positioned in an adjacent upper tier, the bottom projection pushes the elongated member in the groove to secure the geogrid fabric to the block. With this system, it may be possible for a strong force to pull the fabric from between the tiers of blocks.
U.S. Pat. No. 6,019,550 teaches a method for securing a perforated plastic fabric to concrete block earth retaining wall. The blocks are formed with vertical passages which are aligned when the blocks are stacked. Pins are inserted in the passages to prevent the blocks from shifting relative to each other in a horizontal plane. A groove is formed in the top of each block to extend parallel to the face of the block. After a tier of blocks is stacked and backfill is added behind the wall, a geogrid fabric is placed to extend over the top of the blocks and the backfill. A special anchor member is then placed in the groove on top of the fabric. The anchor member includes longitudinally spaced projections which extend through the perforations in the fabric. When the next tier of blocks is stacked on the wall, the anchor member is confined in the groove and secures the fabric to the wall. The anchor member is designed for use with blocks having a top groove sized to receive the anchor member and the fabric and having projections which have the same longitudinal spacing as the spacing between perforations in the fabric. Also, it is necessary to align the fabric with the wall blocks so that a row of perforations are positioned to receive the anchor member when the anchor member is inserted into the groove in the top of the blocks.
U.S. Pat. No. 6,679,656 discloses a method for securing a geogrid fabric to a retaining wall formed from stacked blocks. A groove is formed in the top of each block to extend generally parallel to the direction of a wall formed from the blocks. When blocks are stacked to form a lower tier, the grooves on the individual blocks align to form a continuous groove. The geogrid fabric extends from behind the tier where it will be embedded into fill behind the wall. The fabric is wrapped around a rod which is positioned in the groove towards the front of the wall. The free end of the fabric nearest the rod is folded over the rod so that it extends towards the back of the wall. The groove has a sufficient horizontal width to receive two rods and the geogrid fabric. A second rod is then laid in the groove to the rear of the first rod to extend over the fabric. An upper tier of blocks is then stacked over the lower tier so that the groove in the top of the lower tier is covered by the blocks in the upper tier. The weight of the blocks in the upper tiers retain the rods in the groove. Backfill is then added behind the upper tier of blocks to cover and anchor the geogrid fabric. Any force tending to move the retaining wall will place tension on the geogrid fabric in a direction attempting to pull the fabric from between the stacked blocks. This causes the rods to wedge more tightly in the groove to make it more difficult to pull the fabric from between the blocks.